DHW Tank depletes quickly

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Old 12-18-16, 04:52 PM
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DHW Tank depletes quickly

I recently had a Bosch modulating/condensing boiler installed in October with a 30 gallon Buderus Indirect HW Tank. Systems works great but I am having a minor issue with the DHW tank. When using the bath tub the hot water in the tank completely depletes after about 4 minutes. I was told that this should not be the case by the installer, I "should" have plenty of water.

I tried to get the installer to look at it, he came out to my house a month ago to see if he could fix it but he was unsure of what was causing it to deplete so quickly. He told me he would have to reach out to the boiler manufacturer and get back to me. I tried reaching out 4x and he is now just dodging my calls/e-mails.

Before I find another company to come and look at it I figured i'd give the forums a shot.

The DHW has a mixing valve and the tank hot water is set to 145 degrees but the mixing valve turns its output to around 115. My brother in law had the same exact DHW tank installed a few months prior to me and he does not have the same issue as me. He has a standard oil fired burner and no mixing valve.

Thanks!
 
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Old 12-18-16, 05:32 PM
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Not a pro in this area but let me get the ball rolling with a question: Let's say no one is using hot water and the boiler isn't firing for heat or anything. If someone starts running hot water, how long before the boiler begins to fire?
 
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Old 12-18-16, 06:16 PM
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I just tested it and it took 5min 40 seconds using the sink in the bathroom, not the tub.
 
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Old 12-18-16, 06:27 PM
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Make sure the system controls are set up so that the DHW tank is getting "priority" during a HW call.

This is critical on the newer mod/cons, which are designed to operate at lower boiler temperatures, because in addition to giving the DHW pump priority, the boiler also needs to fire to higher temps.
 
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Old 12-18-16, 06:39 PM
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Sounds like check valve issue... crossover...Circ pump ghost flow???
 
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Old 12-18-16, 06:52 PM
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The systems is already set to DHW tank priority
 
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Old 12-19-16, 05:16 AM
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Just curious, your not trying to fill a hot tub,how is it if you take a normal shower?
 
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Old 12-19-16, 05:24 AM
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So, normal shower is fine. Average shower is 10-15 min and we do not run out. Only reason why we noticed the bath depleting so quickly is because when we give my daughter a bath it runs out so fast so we have been trying to get used to turning the tub on/off so it doesn't run out as quickly.

Although yesterday, I was washing dishes for a bit and my wife took a shower and she said she ran out of hot water. So the mixture of me washing dishes and he showering at the same time depleted the tank as well.

It's quite frustrating to run out of water, before my upgrade I had an oil fired burned with a built in cool for DHW and I only ran out of HW on occasion but not like this.
 
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Old 12-19-16, 06:36 AM
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Please give us the model numbers of the boiler and tank.
 
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Old 12-19-16, 08:03 AM
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Boiler- Bosch Greenstar 57 - ZBR16-3
HW Tank- Buderus S32 30 gallon indirect water heater
 
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Old 12-19-16, 01:19 PM
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J,
I know some contractors are installing mixing valves with these tanks and that's fine if you get the recovery but most times you don't and they cut the temp going out too low.

First off you only have a 30 gallon tank. A tub spout with normal house pressure puts out about 7 gals. a minute. That gives you your 4 minutes of hot water if the boiler cannot deliver enough hot water for the tank to recover.

Chances are that is where you are running out and the faucets and shower is fine because of the lower gpm draw. Next delivering domestic hot water at 115 deg. is not much over body temp. and your probably running it straight without much mixing at the faucets and probably not at all when pouring a bath.

Gas fuel burns cooler than oil and is slower recovery. That is why you do not see tankless coils in gas boilers anymore. They just do not perform well so once you start to draw, especially running the tub it will not keep up.

My suggestion is if your going to keep the mixing valve raise the tank temp up to about 160 so you will have more reserve and let the mixing valve reduce the temp to about 130 and do the final mix at the faucet to get the temp you want. That will make you add more cold water at the taps and use less straight hot water from the tank and you will get more out of it.

You can play with the tank temp to suit your needs. You can raise even high if need be as long as the mixing valve is in place and it will give you more reserve.

If you have kids make sure they know of the increase in temp at the faucets and can mix it so as not to get burned. You can also run your tub slower and that would help to give the tank a better chance to recover.

I hope this helps a little.
 
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Old 12-19-16, 02:01 PM
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Increasing the temp at the mixing valve from 115 to 130 won't change how much hot water you have, it will just make it so you are mixing the cold water in at the faucet instead of at the mixing valve, and you'll get more loss from the pipes as they go through the house if they're 130 instead of 120.

Also, 130 degree water is high enough to scald. Keep the mixing valve output to 120 especially if you have kids.

If your indirect can handle 160 degrees as a target, go with that, but keep the mixing valve where it is and you'll get more time before it runs out.

I'm not sure what the greenstar controls are like, but on my buderus, the max dhw temp is 140, and my installer wired everything wrong so it was using the Taco's DHW priority controls, which meant that the heating system pump was running for no reason during every DHW call and was wasting heat.

I was running out when I had the tank at 120 and was using the Taco DHW control. Added a mixing valve, set it for 120, and switched over to the buderus' built-in dhw priority control at 140 tank temperature, i now only run out if i try to fill up the jacuzzi tub... and even then recovery is very quick.
 
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Old 12-19-16, 02:06 PM
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One further thing, you probably want to check this first:

If the DHW isn't wired up properly to defeat the outdoor reset, you might be trying to heat the water tank with 140 degree water instead of 180+... it will take forever to recover if it is running at the reduced/modulated output.
 
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Old 12-19-16, 02:14 PM
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All, thanks for the input. I will confirm what the mixing valve is at and adjust to max 120. As for the tank temperature, isn't is a negative to go up that high in the tank temp? I read somewhere in the manual not to go above 140 or somewhere along those lines due to limescaling. I will report back later on tonight.
 
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Old 12-19-16, 04:17 PM
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mixing valve reduce the temp to about 130
when we give my daughter a bath
If you have kids make sure they know of the increase in temp at the faucets and can mix it so as not to get burned. You can also run your tub slower and that would help to give the tank a better chance to recover.


You have small children I would not be raising the temp up to 130F. Takes seconds to get burned severly..

Just my opinion..

Per specs..

That indirect wants a 88,000 btu boiler to get its continuous rating of 137 gallons per hour.

Thats 2.28 gallons per minute

Your boiler only produces 57,000 k btu max. That there will reduce the ratings. Additionally that indirect wants 8gpm through the coil to meet the full performance data. If your not getting that with what pump the installer put in then that 2.28 gallons a minute get reduced more.

You can convert this all to see what you are getting GPH with the lower BTU and GPM if pump is sized too small..

GPH first hour rating is 165..

Last is the indirect is not piped right off the boiler like here #7 Then that can cause issues too.

Also close space tees are needed at X.. Do you have this?

Name:  boiler tees.jpg
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Last I may have went for a super stor indirect. Contender

HTP - SuperStor Contender Indirect Water Heater

These have a 152 GPH rating ( @ 115F) in the 35 gallon model. AND get this.... At only 53,000 K boiler needed..

Also these need the 8gpm through the coil.

Just some food for thought..
 
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Old 12-19-16, 05:03 PM
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You have small children I would not be raising the temp up to 130F. Takes seconds to get burned severly..

Just my opinion..
Agreed, I will not up it to 130. Unfortunately, I dont think there is a way for me to tell what the temperature is set to. I have a Honeywell AM-1 mixing valve and it doesnt show what the temp is actually set to, I would need a thermal sticker to determine the actual temp.

Last is the indirect is not piped right off the boiler like here #7 Then that can cause issues too.

Also close space tees are needed at X.. Do you have this?
Not 100% sure but I will take a bunch of pictures and upload them for review.
 
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Old 12-19-16, 07:21 PM
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I uploaded the photos to a google photo album, see below for the link

https://goo.gl/photos/tbyeVyhXGWpfNtwu8
 
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Old 12-19-16, 07:47 PM
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That pump on the indirect, what speed is the switch on the side set too?

Also does the pump model say IFC anywhere? internal flow check?
 
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Old 12-19-16, 07:50 PM
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Also looks like that white valve is being throttles at the indirect? That will accomplish nothing... open it up..
 
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Old 12-19-16, 08:00 PM
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The white valve is the DHW out to the house. The installer throttled that when he came to troubleshoot.

As for the circulator pump, I add some photos of it to the same photo album, the switch is all the way up and I didnt see an IFC on the model

Model# is Grundfos UPS15-58FRC
 
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Old 12-19-16, 08:11 PM
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Forgot to mention, the highest the boiler DHW Tank temp can go is 158. Also for the Mixing valve, in order to adjust the temp, do I need to remove the scren then adjust or can I just adjust the knob without removing the screw?
 
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Old 12-19-16, 08:13 PM
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Yes I see... The other pump has the FRC?

All Looks good. Close space tees, proper check valves, etc..

I would now look into the settings you have in the boiler for HW priority...

Dont have time to read the manual tonight... maybe tomorrow..

That boiler must high fire when DHW is call for and all zones shut off...These are things that beed to be checked...

I will mull things around in my brain tomorrow...I may see something else if I look at pics in greater detail..
 
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Old 12-19-16, 08:18 PM
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That looks like a honeywell mixer... some you have to remove the screw as it locks in place... This prevents tampering I have had guys try to turn them and strip the handle...


Look to see is there is a model # on that mixer... It should have check valves too built in...

Do you have a recirc pump on your hot water?
 
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Old 12-19-16, 08:21 PM
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How big is your tub? Big soaking tub or standard?
 
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Old 12-19-16, 08:24 PM
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Recirculator pump at like the farthest sink? No, I wish I did because my kitchen literally can take almost a minute to get hot water.

The mixer is a honeywell, it's a model am1, I will have to see if it has any order model# on there. I was told by the installer I just needed to turn it but after reading the manual I found online it says I need to remove the screw but there are a bunch of different manuals for the same model so it is confusing.

I appreciate all of your help. I ran through the manual and there was a section on the controls in the manual for DHW Priority but I do not have that option on my controls.
 
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Old 12-19-16, 08:27 PM
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AM100-US-1LF - Honeywell-Sparco AM100-US-1LF - 1/2" Lead Free Union Sweat Mixing Valve, 70-145F


AM-1 Union STD & C and AM1070 Models include check valves(hot/cold ports)
 
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Old 12-19-16, 08:28 PM
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I appreciate all of your help. I ran through the manual and there was a section on the controls in the manual for DHW Priority but I do not have that option on my controls.
stand by..... .
 
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Old 12-19-16, 08:28 PM
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How big is your tub? Big soaking tub or standard?
Standard Tub, it runs out of hot water about a 1/3 of the way up the tub.
 
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Old 12-19-16, 08:31 PM
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Whats pressure gauge read on boiler? These units need to run at higher pressures...( Gauge behind front door)

The standard boiler water pressure is 14.5 - 21.75 psi (1 - 1.5 bar).

http://www.prowaterheatersupply.com/...ers_Manual.pdf
 
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Old 12-19-16, 08:35 PM
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It's just above 15psi, added pic to album...
 
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Old 12-19-16, 08:36 PM
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Take pic of boiler with front door open so I can see the controls...

Do you have outdoor reset? The guy should have installed a module outside thats attached to the boiler with wires
 
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Old 12-19-16, 08:38 PM
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You should have eco mode button..


ECO button
Pressing and holding the ECO button until it lights up switches between Comfort
mode and Economy mode.
Comfort mode, ECO button is not lit (default setting)
In Comfort mode, the DHW tank has priority. The DHW tank is heated to the set
temperature first. Then the appliance switches to central heating mode.

Economy mode, ECO button lit
In Economy mode, the appliance alternates between central heating mode and
DHW mode.
 
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Old 12-19-16, 08:40 PM
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Yes, I have outdoor reset, I actually ran the wiring for the outdoor reset unit . Eco button is not lit, I'll take a pic in a minute
 
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Old 12-19-16, 08:47 PM
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what heat emitters are in the home? Copper baseboard? Radiators?
 
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Old 12-19-16, 08:50 PM
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Uploaded the photo, I have all baseboard heat. No radiant
 
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Old 12-19-16, 08:59 PM
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I see this in the controls... Might want to look into what that means..

Install Manual

http://www.prowaterheatersupply.com/...ion_Manual.pdf

Page 61

Service function 3.d: Minimum output (heating and DHW)
The output for heating and DHW can be set to any level in percent
between the minimum and maximum nominal output.
The default setting is the minimum nominal output (heating and DHW)
and varies according to appliance.
So if you run the tub and use a lot of hot water the next thing to look at is the screen on the boiler..you want to see if its fireing at 100 % and what temp the boiler is working at...

Also dial on left should be turned all the way to max...( For baseboard)
 
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Old 12-19-16, 09:06 PM
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I'll adjust the knob on the left to put it all the way up.

I'm not understanding the nominal output setting. What percentage should it be set to?
 
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Old 12-19-16, 09:06 PM
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Thats all I got for tonight... have to go to bed... 5 am start tomorrow.

Oh and a note... your pics link to your GPS from your phone and show exactly where you live.. With map and all...

I would fix that for security purposes...
 
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Old 12-19-16, 09:08 PM
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I'm not understanding the nominal output setting. What percentage should it be set to?
I would say 100% for DHW?? ( Im assuming) But I would probably call tech support and ask the boiler manufacturer before I touch the controls... If there is such a setting...

Hence why I asked for you to see how the boiler fires and temps during a call for DHW...From that you can determine whats going on...
 
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Old 12-19-16, 09:12 PM
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Thanks, I took down the album. I'll call Bosch to see what they say. Appreciate your help!
 
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